US7099329B1 - Method for preventing overload condition in a circuit switched arrangement - Google Patents
Method for preventing overload condition in a circuit switched arrangement Download PDFInfo
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- US7099329B1 US7099329B1 US10/026,079 US2607901A US7099329B1 US 7099329 B1 US7099329 B1 US 7099329B1 US 2607901 A US2607901 A US 2607901A US 7099329 B1 US7099329 B1 US 7099329B1
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L47/00—Traffic control in data switching networks
- H04L47/70—Admission control; Resource allocation
- H04L47/82—Miscellaneous aspects
- H04L47/822—Collecting or measuring resource availability data
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L47/00—Traffic control in data switching networks
- H04L47/10—Flow control; Congestion control
- H04L47/15—Flow control; Congestion control in relation to multipoint traffic
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L47/00—Traffic control in data switching networks
- H04L47/70—Admission control; Resource allocation
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L47/00—Traffic control in data switching networks
- H04L47/70—Admission control; Resource allocation
- H04L47/74—Admission control; Resource allocation measures in reaction to resource unavailability
- H04L47/745—Reaction in network
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L47/00—Traffic control in data switching networks
- H04L47/70—Admission control; Resource allocation
- H04L47/76—Admission control; Resource allocation using dynamic resource allocation, e.g. in-call renegotiation requested by the user or requested by the network in response to changing network conditions
- H04L47/765—Admission control; Resource allocation using dynamic resource allocation, e.g. in-call renegotiation requested by the user or requested by the network in response to changing network conditions triggered by the end-points
Definitions
- This invention relates to a method for preventing, or mitigating the effects of, an overload condition in a circuit switched telecommunication network.
- a network includes one or more arrangements where a group of client terminals are statistically multiplexed onto one or more transmission paths, the signals of active ones of the terminals are brought to a head end terminal (HET), and those signals are then communicated from the head end terminal to a central office switch of the network (henceforth, near-end office) over a shared transmission path.
- HET head end terminal
- HFC circuit switched telephony over hybrid-fiber coax
- PBX circuit switched telephony over hybrid-fiber coax
- terminals that are connected to the PBX are not employing a shared transmission resource in order to reach the PBX.
- central office switch concentrators In the context of this disclosure, therefore, a concentrator at the ingress of a near-end switch is considered to be a head end terminal.
- the near-end office provides the basic functions needed to establish connections, such as dial tone, digit detection, etc.
- Employing the dial tone generation and digit detection circuitry of the near-end office simplifies the architecture and reduces cost by avoiding duplication of features both at the HET and the near-end office.
- the disadvantage of this arrangement is that when circuits in the shared transmission path are congested, new callers cannot connect to the near-end office and, therefore, do not even get a dial tone. Consequently, dialing digits are not transmitted by client terminals (or, if transmitted, are not received) and that leads to difficulty in implementing intelligent admission controls.
- the above describes one source by which congestion can occur at, or prior to, the near-end office.
- congestion can occur, simply because of an extraordinary use of the near-end switch in response to some event, such a radio “call-in” contest. That can occurs of course, when components of that near-end switch that are shared, such as a concentrator or a digit collector, become overloaded. It might also be caused by a large number of computer users whose computers automatically keep redialing a busy Internet Service Provider (ISP) modem bank in an effort to obtain a modem the moment one becomes free.
- ISP Internet Service Provider
- the central network i.e., the network core excluding the near-end offices and their connections to users
- the central network is often protected from some of these overload conditions by means of a “choke” network.
- This is typically implemented with a limited number of trunks that are set up in a trunk group specifically for a “call-in” contest telephone number. Once these trunks are busy, the switch returns a re-order tone (fast busy) to any additional user attempting to access the “call-in” number.
- the end offices themselves are, however, not protected from rapid retries, except in the sense that a user is likely to give up after a few busy signals.
- Congestion problems in prior art networks are alleviated, and an advance in the art is achieved, with an arrangement that includes a number of signaling channels, over and above existing out-of-band signaling channels, that are used for congestion control.
- the improved arrangement converts one or more of the communications channels to one or more groups of enhanced signaling channels.
- congestion control is effected by employing the enhanced signaling channels, which can carry audible signals, to determine whether to set up requested calls, based on a preselected congestion control process.
- FIG. 1 illustrates a physical arrangement of a network switch that is coupled to terminals directly, as well as indirectly, through a head end terminal;
- FIG. 2 describes two curves that may be employed in a congestion control method for the FIG. 1 arrangement, which works to assure an always existing capacity for attempting new calls;
- FIG. 3 presents a flow diagram of a method where a predetermined number of channels are reserved in the FIG. 1 arrangement for real-time communication;
- FIG. 4 presents a flow diagram of a method for delaying dial tone to terminals with an excessive number redial attempts
- FIG. 5 presents a structure useful for implementing the FIG. 4 process
- FIG. 6 presents a method for providing telecommunication services to terminals in the FIG. 1 arrangement, with dedicated signaling channels on path 30 ;
- FIG. 7 presents block diagram of one embodiment for carrying out the FIG. 6 method.
- FIG. 8 presents block diagram of another embodiment for carrying out the FIG. 6 method.
- FIG. 1 presents a diagram of an illustrative arrangement where the principles disclosed herein can be practiced.
- switch 10 (with processor 11 ), which is a near-end switch of a network that, on the trunk side, is connected to other switches of the network.
- Terminals 41 and 42 are connected directly to switch 10 , as well as ISP 40 .
- shared path 30 connects HET 20 to switch 10 .
- HET 20 includes a processor 21 that performs all of the processing needed in HET 20 .
- Terminals 45 – 46 are connected to HET 20 via path 51
- terminals 43 – 44 are connected to HET 20 via path 52 .
- Paths 51 and 52 may be, for example, hybrid-fiber coax systems, shared among the terminals.
- terminals 43 – 46 are termed “downstream” terminals, and paths 51 and 52 are termed “downstream” paths.
- HET 20 concentrates the signals on each of the downstream paths (multiplexing action) and further concentrates the signals of the downstream paths onto shared transmission path 30 (also multiplexing action), and correspondingly demultiplexes signals on their way from shared path 30 .
- the following discloses a number of methods for protecting the FIG. 1 arrangement from overload.
- This method protects against transmission path congestion that, without some imposed access controls, can block access to switch 10 to the point that dial tone cannot reach a downstream terminal that seeks to initiate a call. This applies to congestion on paths 51 and 52 as well as to congestion on path 30 .
- a call can be conceptually divided into an initial “attempt” period and a subsequent “communication” period.
- a downstream terminal receives a dial tone from switch 10 and forwards dialed number digits to switch 10 .
- the communication period begins when switch 10 effectively accepts the call by starting to route the call to the dialed number.
- the method contemplates that at all times, with very high probability, an available (i.e., unoccupied) channel exists on the paths 30 and 51 transmission medium and on the paths 30 and 52 transmission medium, and that a mechanism is provided to assure this.
- any downstream terminal coupled to path 51 (or coupled to path 52 ) that wishes to initiate a call is granted one of the available path 51 (or path 52 ) channels and one of the available path 30 channels, receives a dial tone from switch 10 , and proceeds to forward dialed number digits; i.e., engages in a call attempt.
- near-end office 10 decides whether or not to drop a call.
- the call dropped is a call that uses a channel on path 30 and a channel on one of the downstream paths.
- the set of calls that are considered for dropping includes all calls in the midst of their communication period as well as all calls in the midst of their attempt period. Some calls, on the other hand, may be exempt from such forced dropping, for example, 911 calls.
- a call is dropped when either one of the two decisions is to drop a call. Stated in other words, if a conclusion by a component decision to drop a call is designated by a logical “1”, then the final decision of the method is the logical OR function of the two component decision logical values.
- the OR function when the first component decision that is made corresponds to logical “1,” the second component decision does not need to be undertaken.
- One embodiment of this mechanism employs two threshold values, for example, K 2 and K 1 in connection with path 30 .
- K 1 When remaining capacity is larger than K 1 , no calls are dropped; when capacity is between thresholds K 1 and K 2 (inclusive of K 2 and K 1 ), a first algorithm is employed in the decision to drop a call; and when remaining capacity falls below K 2 , a second algorithm is employed in the decision to drop a call.
- K 1 and K 2 inclusivee of K 2 and K 1
- FIG. 2 presents a curve 41 that embodies one implementation of the mechanism, which corresponds to a probabilistic approach to the drop/no drop decision.
- capacity on path 30 is greater than K 1 , the probability of a decision to drop a call is zero.
- capacity on path 30 is equal to or less than K 1 but also equal to or greater than K 2 , the probability of a decision to drop a call is between zero and 1 and increasing toward 1 as capacity decreases.
- remaining capacity on path 30 is less than K 2 , the probability of a decision to drop a call is one (i.e., a certainty).
- the probability curve between K 1 and K 2 need not be linear and that, in fact, one can dispense with the explicit thresholds K 2 and K 1 by employing an appropriately selected probability function, such as the one depicted by curve 42 . In practice, however, employing thresholds K 2 and K 1 results in a lower computational burden.
- a similar two-threshold scheme may be employed over paths 51 and 52 to control congestion on those paths.
- the parameters set may be set differently for different paths.
- a selection of the call to be dropped must be made.
- the set of calls from which a call to be dropped is selected comprises all calls on path 30 (those in the midst of their attempt period and those in the midst of the communication period).
- the set of calls from which a call to be dropped is selected comprises all calls on the downstream path to which the terminal making the call attempt is connected.
- data call as used herein is illustrative of, and encompasses, all calls where persons using the FIG. 1 arrangement do not necessarily expect real-time transmission of information.
- voice call as used herein is illustrative of, and encompasses, all calls where persons using the FIG. 1 arrangement do expect real-time transmission of information.
- the processor needs to know about the available (i.e., remaining, unoccupied) capacity on path 30 and about the available capacities on paths 51 and 52 .
- Switch 10 knows the remaining, unoccupied, capacity on path 30 because the path is coupled directly to processor 11 .
- HET 20 must inform processor 11 of the maximum capacity on the downstream paths, if the maximum capacity is alterable, and processor 11 must know which downstream terminals are coupled to which downstream paths. Since a call attempt identifies the downstream terminal that is making the call attempt, it follows that a lookup table in processor 11 associating downstream terminals with downstream paths would do. Alternatively, of course, HET 20 can identify to switch 10 the downstream path from where the call attempt is made, as the attempt is being made.
- processor 11 needs to have the ability to drop calls in switch 10 and to cause HET 20 to drop calls and release corresponding channels on the downstream path of the dropped calls. That capability is inherent in the normal operation of the FIG. 1 switch 10 and in the normal switch 10 —HET 20 interactions. That is, any signaling interface that is employed between switch 10 and HET 20 for the normal operation of the FIG. 1 arrangement, such as GR.303 or TR.303, can be used to implement the signaling needs of this method.
- processor 11 must have the necessary information for making the call selection. For some of the decision schemas listed above, in connection with each of the calls that is included in the set of calls from which a call to be dropped is selected, processor 11 needs to know the call's type and duration. Knowledge of a call's duration is, again, inherent in the normal operation of switch 11 , but the call's type—that is, whether the call is a data call or a voice call—is not.
- a call's type can be ascertained from one or more of the following call attributes: (a) calls that carry “modem tones” are data calls, and (b) calls that are marked by periods of relatively low power are voice calls (such low power periods result from breathing pauses and/or normal conversation patterns where one person speaks for some time while the other is quiet, and vice versa).
- a call's type can be sometimes ascertained—in the case of both established calls, and calls that are in the midst of their attempt period—from (c) the called number, and (d) the calling number.
- Information that imparts a call type based on calling and called number can be provided to processor 11 , or can be derived by processor 11 from accumulated (historical) information.
- An example of (c) is a called number that is known to be a modem pool of an Internet Service Provider (ISP), or from a home office telephone line that is known to be used for computer communication.
- An example of (d) is a home line that is found to be used exclusively by a computer, or almost exclusively, from prior determinations of the call type that the particular calling party terminal carried.
- processor 21 must have the same information, and the same control capabilities that are needed in processor 11 and that are described above. That is not a problem because processor 21 can easily keep track of the spare capacity on path 30 , naturally keeps track of the spare capacity on paths 51 and 52 , and inherently has the capability to drop calls. Also, call-type information can be obtained from processor 11 , or compiled locally by processor 21 . Of course, processor 21 must also have the capability to perform the necessary computations and decisions, but those capabilities are quite modest for this method.
- switch 10 may be directed to first terminate an ongoing call and only then determine whether the incoming call attempt should be accepted. This provides some additional protection against overload due to near simultaneous call attempts. That is, this approach increases the probability that the spare capacity on path 30 will not fall below K 1 but, on the down side, it may terminate a call that did not need to be terminated.
- K 1 is chosen to be significantly less than the capacity of shared transmission path 30 and that, normally, the number of available circuits will not drop below K 1 because the above algorithm may drop a call whenever a call attempt is made and the capacity is less than K 1 (i.e., drops a call in the sense that it drops a call in the midst of its communication period or a call in the midst of an attempt period).
- K 1 is chosen to be significantly less than the capacity of shared transmission path 30 , that possibility is extremely remote, but theoretically possible.
- path 51 is a shared resource that can be overloaded
- path 30 is a shared resource that can be overloaded.
- the described example comprises two shared overloadable resource arrangements, where a shared overloadable resource (SOR), or an overloadable resource (for short), is a resource that, when employed with respect to a call, has an resource element occupied for the duration of the call, such as a communication channel.
- SOR shared overloadable resource
- an overloadable resource for short
- Arrangement 1 includes SOR 1 30 , which is the first member of the arrangement—that being path 30 , and SOR 1 51 , which is the second member of the arrangement—that being path 51 .
- Arrangement 2 includes SOR 2 30 , which is the first member of the arrangement—that being path 30 , and SOR 2 52 , which is the second member of the arrangement—that being path 52 .
- Path 30 has Q 30 resource elements
- path 51 has Q 51 resource elements
- path 52 has Q 52 resource elements.
- HET 20 could constitute an SOR by virtue of the fact that processor 21 may be placed in overload, and other components within HET 20 may also be statistically multiplexed.
- the above disclosure focuses on the elements that are coupled to near-end office 10 and that use the near-end office as a gateway to the telecommunications network.
- the principles disclosed herein are applicable to elements within the network as well.
- that end office 10 is connected via a trunk group to a particular toll or tandem switch. If the trunk group is nearly full (or in overload), beneficial result are achieved by engaging a process that, in response to a need to place an additional call on that trunk group, considers whether to drop an existing call that is serviced by that trunk group.
- Either near-end office 10 or the toll/tandem office can do the selective dropping but, normally, it would be preferable for the end offices to do this, for reasons of load and processing capability of the processors within the near-end office on the one hand, and the toll/tandem office on the other.
- a reasonable criterion for a call to be terminated is that it goes through a relatively large number of hops and therefore uses an unusually large amount of network resources. Dropping such a call is useful because by dropping a single call several other calls may be allowed to proceed.
- the AT&T toll network uses an algorithm called Real Time Network Routing (RTNR) that allows calls to be one or two hop.
- RTNR Real Time Network Routing
- Approximately 5% of the links are reserved for one-hop calls because it was found that, without some reservation for one-hop calls, the network could become stable with almost all calls being two-hop calls, and this severely restricts network capacity.
- RTNR Real Time Network Routing
- no reservations are needed because one can drop the two-hop calls when necessitated by network load conditions.
- a very heavily loaded network would rapidly migrate toward all one-hop calls, yielding maximum call handling capability.
- the method disclosed herein works better for all network load conditions. It may be noted that one could also drop calls based on multiple hops (i.e., more than two), and on expected long holding times; for example, calls to 800 numbers that normally have long queues of people waiting to talk to a representative are calls with expected long holding times.
- This method focuses on the type of the calls that are carried by the shared overloadable resources and, more particularly, focuses on retaining or dropping calls based on priority notions related to the types of calls under consideration, in an effort to insure that at least a certain, predetermined number of channels are reserved for use in connection with a certain type, or types, of communication.
- calls are divided into two classes of calls: voice and data, and the reservation is for a certain number of voice calls. More specifically, for the illustrative embodiment of this method, which is disclosed below for the FIG. 1 network arrangement, the method reserves K 30 channels for voice communication on path 30 , K 51 channels for voice communication on path 51 , and K 52 channels for voice communication on path 52 .
- the FIG. 3 method is carried out seriatim for each SOR in the serial connection of the SORs in the FIG. 1 arrangement that is relevant to the terminal that went “off-hook” and seeks to establish a connection. For example, when telephone 45 seeks a connection, the available, unoccupied, capacity on path 51 is assessed, and if the assessment does not result in a call being dropped, the available, unoccupied, capacity on path 30 is assessed.
- step 226 determines whether the unoccupied capacity exists on each of the links that lead to switch 10 .
- N a number of voice call
- K V the number of voice calls that are reserved for the path
- control passes to step 225 which processes the call.
- step 223 determines whether the call sought to be established is a voice call.
- step 223 determines that the call sought to be established is a voice call
- step 224 which drops the call that is sought to be established.
- Another embodiment of this invention does not simply drop the incoming, sought to be established, call when step 226 determined that unoccupied capacity does not exits, which means that one or more of the serially connected overloadable resources between the terminal that wishes to be connected to, say, switch 10 , is fully occupied. Rather, in such other embodiment, higher priority calls, for example, voice calls, can be allowed to be established but, of course, at a cost of some lower priority established call, for example, a data call, being dropped. This implies that the terminal seeking connection at least is made known to the apparatus that carries out this method.
- the disclosed method II which incorporates all the teachings of method I, can be carried out in processor 11 as well as in processor 21 , because all information that is known to processor 21 is also known, or can be provided to, processor 111 ; and all necessary controls that are available to processor 21 are also available to processor 11 , directly or indirectly.
- the method carried out in processor 11 is only slightly different from the method carried out in processor 21 .
- the first test might be to determine whether the call that is sought to be established is a voice call. If so, it is processed. Otherwise, the call is processed only if the number of established data calls is less that the maximum number of allowed data calls, determined by considering the maximum number of calls that a path can service, less the number of calls reserved in that path for voice.
- This method focuses on overload conditions resulting, at least in part, from repeated redialing.
- the basic idea is that if a particular telephone line redials a previously busy number within a short period of time, the chances are good that the number will be found to be still busy.
- FIG. 4 One embodiment of this method is illustrated in FIG. 4 . As with the methods disclosed above, this method can be carried out in processor 11 (encompassing all terminals that are connected to switch 10 ) as well as in processor 21 (encompassing all downstream terminals). An illustrative processor 11 embodiment is depicted in FIG. 4 .
- step 201 When an off-hook condition is detected from a terminal, control is asserted by step 201 , which identifies the calling number of the terminal that went off-hook and determines, by reference to a database file in switch 10 , whether the calling number is found in a set of calling numbers that have been excluded from experiencing delays.
- the calling numbers in such a file might correspond to very important persons, to people who pay a premium for their service, to telephones of emergency services, etc.
- the same database look-up optionally obtains information about whether the off-hook terminal has employed an automatic re-dialer in the past, and about the last time that the off-hook terminal attempted to get a dial tone. Also, information may be optionally retrieved as to whether the last time the terminal dialed resulted in an established call; and if not, whether the failure was caused by a trunk busy condition, or a “called party busy” condition.
- step 201 determines that the calling number is not permitted to have its dial tone delayed
- control passes to step 213 , which provides a dial tone and accepts dialed digits.
- step 201 determines that the calling number is permitted to have its dial tone delayed
- control passes to step 202 , which may optionally conclude that the off-hook terminal is not a retry, e.g., when the database look-up indicates that the last off-hook condition for this terminal resulted in a completed connection. If the attempt is a suspected retry, then control then passes to step 203 , which determines, also from the database look-up, whether the time interval between the current attempt and the last attempt is greater than some preselected threshold, T 1 .
- step 203 An affirmative conclusion in step 203 is treated as a new call (though, in fact, it may be a redial attempt) and control passes to step 213 .
- a negative conclusion in step 203 is treated as a possible redial attempt (though it is recognized that the off-hook terminal may desire to attempt establishing a call to a new called number).
- control passes to step 204 , which increments a “retry” counter.
- Control passes to step 205 , which compares the value of retry counter N to a preselected number, K—which corresponds to the number of retries that are permitted without an introduction of a dial tone delay. When N is less than or equal to K, control again passes to step 213 ; otherwise control passes to step 206 .
- step 206 evaluates the time interval between the current off-hook condition and the previous off-hook condition (assessing how long ago was the last dialing attempt), or the previous on-hook condition (assessing how long was the last “call”). When it is concluded that the time interval is less than or equal to T 1 but greater than T 2 (where T 2 is less than T 1 ), step 206 concludes that the off-hook condition corresponds to a simple redial attempt. Thereupon, control passes to step 207 , which sets variable a to a first value, ⁇ 1, and then proceeds to step 209 .
- step 206 concludes that the off-hook condition also corresponds to a redial attempt, but by a particularly anxious terminal that is likely to attempt redialing very often. Responsively, control passes to step 208 , which sets a to a value, ⁇ 2, that is larger than ⁇ 1 (imposing a longer delay), and then proceeds to step 209 .
- Step 209 determines from the database look up whether the off-hook terminal used a re-dialer in its last attempt. When that is the case, step 210 increases the value of ax and passes control to step 211 . The value of a is increased in order to lengthen the dial tone delay, because it is expected that terminals that use re-dialer are likely to repeat redialing attempts very often, if given a chance. As an aside, use of a re-dialer is identified through analysis of the duration of the dialing sequence and the uniformity of its timing.
- Step 211 introduces a congestion factor. Illustratively, it multiplies ⁇ by (F 1 ⁇ F 2 ⁇ F 3 ), where F 1 corresponds to a trunk busy condition, F 2 corresponds to “called party busy” condition, and F 3 corresponds to the general congestion level in switch 20 .
- F 1 1.2 when the last attempt was unsuccessful due to a trunk busy condition, and 1 otherwise
- F 2 1.5 when the last attempt was unsuccessful due to a “called party busy,” and 1 otherwise
- F 3 starts at a value of 1 when switch 10 is lightly loaded, and increases with the load of switch 10 .
- step 212 calculates a dial tone delay value by multiplying N by ⁇ , and imposes the calculated delay before it passes control to step 213 .
- step 213 provides a dial tone to the terminal that went off-hook.
- step 213 information is collected about the dialing attempt and its consequences in step 214 , and that information is stored for the aforementioned database look-ups.
- the called party's number can be stored and used in the decisions regarding dialing.
- retry attempts to emergency numbers may be excluded from any delays.
- retry attempts to heavily dialed numbers such as radio call-in programs, of ISP modem banks, may be subjected to longer delays (larger values of ⁇ ).
- the above-disclosed method can be said to be partially blocking redial attempts.
- the number of redial attempts is reduced simply by virtue of the delay, by virtue of an increased probability that the busy condition that causes the redial attempt has disappeared, and by encouraging some attempts to be given up entirely. Fewer redial attempts reduce the load on the communication channels of switch 10 , and that is the salutary effect that is desired.
- the method carried out in processor 21 is basically the same as the method depicted in FIG. 4 . It should be noted that the various functions disclosed in connection with FIG. 4 are illustrative, and that other functions can be used with equally good results.
- the above disclosure focuses on the elements that are coupled to near-end office 10 and that use the near-end office as a gateway to the telecommunications network.
- the principles disclosed herein are applicable to elements within the network as well.
- the network switches that are traversed from a calling number to a called number. From the common signaling channel (e.g., Signaling System 7) these switches know the calling number and the called number and when the trunks that need to be employed to form the connection between the calling and called numbers are heavily loaded, the switches can choose to delay providing the necessary path leg if the switches conclude that the call to be established is a redial attempt.
- This method can be carried out in each of the switches within the network (that are involved with a call), even if the end office isn't busy and therefore gave the customer a dial tone without any delay.
- Such an embodiment of the principles disclosed herein could prove useful in avoiding a waste of resources when certain 800 numbers that are nearly always busy are called.
- Method III above discloses an approach for controlling congestion that arises from repeated redialing, where the method imposes a delay on the provision of a dial tone to the terminal that repeatedly redials, as a way for protecting OSRs from congestion (such as path 30 , paths 51 and 52 , and processors 11 and 21 ).
- repeated redialing attempts can impose an undue burden on the means that provides dial tone to terminals and detects dialed numbers, because such means are also an overloadable shared resource. This condition is well known in the central office art.
- method III discloses a process by which a delay is imposed on the provision of a dial tone to terminals that are repeatedly retrying to establish a call. Moreover, the imposed delay is not uniform, and there are numerous factors that affect the length of the delay. Consequently, the lengths of the delays that method III seeks to impose can be quite varied.
- the durations of dial tone delays that are imposed on repeated redial attempts are quantized to a limited number of different delays.
- Implementation of the delays in such embodiments can take the form of separate queues for each one of the different delays, as shown, for example, in FIG. 5 , which is illustrated for step 213 of a method III embodiment that is carried out in processor 11 .
- indication of the terminal that wishes to receive a dial tone is applied to distributor 61 , where it is routed based the value of delay, D, that is computed in step 212 .
- D delay
- queue 62 which is associated with providing zero delay, just like conventional dial tone queues of central office switches is preferably a LIFO queue.
- all of the other queues ( 67 – 69 ), which provide an imposed delay, are preferably FIFO queues.
- selector 63 that, under control of processor 11 selects the output of one of the queues for pairing up with an available dial tone generator and dialed number detector.
- the selection schema for element 63 can vary, and one such schema selects the output of queue 62 whenever that queue is not empty, then selects the output of queue 67 whenever that queue is not empty, then selects the output of queue 68 whenever that queue is not empty, and so forth.
- Various other weighted polling schemes may be implemented, and these can be devised by one skilled in the art.
- An out-of-band signaling channel for purposes of this disclosure, is a channel that does not carry what is commonly referred to as audible signals. Examples of the latter are dial tone, voice, DTMF signals.
- the additional signaling channels which are not out-of-band because they may carry audible signaling, are created from one of more communication channels that in the arrangements described earlier were employed for communication between, for example, terminal 46 , and terminal 42 .
- these additional signaling channels are referred to herein as enhanced signaling channels.
- the enhanced signaling channels do not require the bandwidth that is available in these one or more communication channels that are used to create the enhanced signaling channels, each such communication channel is divided into a plurality of subchannels—using, for example, time division multiplexing—to form the enhanced signaling channels.
- the enhanced telephony signaling is provided on the path between HET 20 and switch 10 in the FIG. 1 arrangement but, of course, it can be provided on other paths, such as on paths 51 , or 52 , or both.
- the FIG. 1 arrangement is an arrangement where a notion of a connection exists that requires a distinct call set-up, and this is one aspect that differentiates the FIG. 1 arrangement from some other networks, or arrangements.
- FIG. 6 The general processing of this method, illustrated for an arrangement where control of access to switch 10 is primarily vested in processor 11 , is depicted in FIG. 6 .
- a FIG. 1 terminal goes off-hook, for example, terminal 45 , that condition is detected in HET 20 and communicated to processor 11 via one of the enhanced signaling channels between HET 20 and switch 10 .
- Step 240 determines whether capacity exists on path 30 and on path 51 , and if the determination is in the affirmative, control passes to step 243 , where a communication channel is assigned in both paths, the off-hook terminal is coupled to switch 10 via the assigned channels, and the call attempt proceeds.
- the congestion control either drops an existing call or not, and passes control to step 242 .
- Step 242 determines whether capacity now exists, and if so, control passes to step 243 . Otherwise, control passes to step 244 , which declines to service terminal 45 .
- dedicated signaling facilities are employed in the transmission medium between HET 20 and switch 10 .
- the signaling passed through the enhanced signaling channels can employ any one of the known protocols, such as SS7 Common Channel Signaling protocol.
- FIG. 7 presents a block diagram showing the pertinent circuits of HET 20 that implement this method (for path 30 ), simplified to represent all channels in transmission path 30 as separate wires, and all downstream terminals that are connected to HET 20 via paths 51 and 52 also as separate wires.
- path 30 is depicted in FIG. 1 by a single line, and is depicted in FIG. 6 by a plurality of lines, the actual, physical embodiment of path 30 may comprise one or more distinct physical transmission elements (wires, cables, fibers). More specifically, embodiments exist where path 30 is a single physical transmission element over which information flows in time slots. One or more of the time slots are devoted to the out-of-band signaling and the remaining time slots are conventionally devoted to voice communication channels. In accord with the principles of this method, one or more of the communication channels are divided into subchannels that form the enhanced signaling channels.
- circuit 22 is for signaling, while switch 23 is for communication.
- circuit 22 establishes a transmission path between each downstream terminal and switch 10 , via lines 24 and 25 (each representing a communication channel that is used for the enhanced signaling channels) and selector element 26 , which is connected to the channels of transmission path 30 .
- the number of channels in transmission path 30 is less than the number of downstream terminal lines coming to elements 22 and 23 ( 10 shown), to illustrate the concentration function that HET 20 performs.
- the FIG. 6 can use fewer or more of the available channels for signaling purposes and that the use of the two channels ( 24 and 25 ) is merely illustrative. Indeed, the number of such signaling channels can be variable, controlled by processor 21 through operation of multiplexer 22 and selector 26 , to accommodate the load that is offered to HET 20 .
- Switch 23 routes accepted call requests of the downstream terminals to switch 10 , also via selector element 26 .
- switch 10 In operation, when a downstream terminal goes off-hook, that information is passed to switch 10 via an enhanced signaling channel of multiplexer 22 and extended through selector element 26 .
- Switch 10 provides a dial tone to the downstream terminal via the same timeslot, and the downstream terminal proceeds to output dialing signals. Those signals are applied to switch 10 , again through the same time slot, and in response thereto, switch 10 proceeds pursuant to FIG. 6 , as disclosed above.
- FIG. 8 Another embodiment, depicted in FIG. 8 , has multiplexer 22 replaced with element 27 , element 26 is eliminated, only one communication channel of transmission path 30 (“wire” 24 ) is employed for the enhanced signaling channels between element 27 and switch 10 , and switch 23 is connected directly to the remaining communication channels of transmission path 30 .
- Element 27 implements the multiplexing function of element 22 , and also includes a processing capability. In this embodiment, the FIG. 6 method is carried out primarily in processor 21 .
- element 27 generates and provides all of the signaling that switch 10 normally sends to downstream terminals (such as dial tone, dialed digits detection, busy signal, “fast” busy), and analyzes all of the signaling that the downstream terminals might wish to send to switch 10 .
- connection between element 27 and switch 10 thus carries only the ultimate information that must be communicated between switch 10 and the downstream terminals (advantageously in digital form) and, therefore, the connection between element 27 and switch 10 needs truly little bandwidth. It is for this reason that only one channel of transmission path 30 is needed between element 27 and switch 10 .
- a “busy” can mean a non-responding server, or one that is server busy and responds very slowly. To identify this condition, the end router has to snoop on packets flowing from the server to find the server's busy condition, and would need to use a timer to determine when the server is not responding.
- the end-router could communicate the busy condition of the server to the originating router, and the originating router could then delay admission, which is the equivalent of delaying dial tone, of subsequent, closely spaced, attempts to the same server.
- the notion of dropping a data call can be extended to not only doing a full disconnect, but also to suspending the flow of packets for, perhaps, a second to allow other connections to proceed.
- the idea of a large hop count still applies.
- the product of the hop count multiplied by the bandwidth required is a figure of how much network resource is being used, and connections where this product is very high are prime candidates for being dropped or suspended. This, again, will cause an overloaded network to tend toward short hop calls, thereby mitigating the network overload.
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Abstract
Description
-
- calls involving two or more channels in the resource that triggered the decision to drop a call.
- Oldest data call from the set of existing data calls.
- Oldest data call from the set of existing data calls, but only if its elapsed holding time is larger than N seconds.
- Oldest call of any type.
- Oldest call of any type, but only if its elapsed time is larger than N seconds.
- A random data call.
- A random data call, from the set of calls with elapsed holding time larger than N seconds.
- A random call.
- A random call, from the set of calls with elapsed holding time larger than N seconds.
A call that finished its attempt period, but waiting to start communication with called party.
-
- a line ID that is to receive no delay is routed to queue 62;
- a line ID that is to receive a small delay (for example, between 0 and 0.4 seconds) is routed to delay
element 64 that, after a delay of 0.4 seconds outputs the line ID to queue 67; - a line ID that is to receive a longer delay (for example, greater than 0.4 second, and up to 1 second) is routed to delay
element 65 that, after a delay of 1 second outputs the line ID to queue 68; and - a line ID that is to receive a still longer delay (for example, greater than 1) is routed to delay
element 65 that, after a delay of, for example, 3 seconds outputs the line ID to queue 69.
Claims (35)
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US10/026,079 US7099329B1 (en) | 2001-06-21 | 2001-12-22 | Method for preventing overload condition in a circuit switched arrangement |
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US29983601P | 2001-06-21 | 2001-06-21 | |
US29983201P | 2001-06-21 | 2001-06-21 | |
US29986001P | 2001-06-21 | 2001-06-21 | |
US32476001P | 2001-09-25 | 2001-09-25 | |
US10/026,079 US7099329B1 (en) | 2001-06-21 | 2001-12-22 | Method for preventing overload condition in a circuit switched arrangement |
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US20080059554A1 (en) * | 2006-08-29 | 2008-03-06 | Dawson Christopher J | distributed computing environment |
US20120039167A1 (en) * | 2010-08-10 | 2012-02-16 | Qualcomm Incorporated | System, apparatus, and method for improving redial performance in wireless communication systems |
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US6404887B1 (en) * | 1998-06-24 | 2002-06-11 | Mci Communications Corporation | Intra-call control of ancillary telecommunications equipment |
US6731740B1 (en) * | 2001-06-21 | 2004-05-04 | At&T Corp. | Method for preventing overload condition in a circuit switched arrangement |
US6826273B1 (en) * | 2001-06-21 | 2004-11-30 | At&T Corp. | Method for preventing overload condition in a circuit switched arrangement |
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US5570355A (en) * | 1994-11-17 | 1996-10-29 | Lucent Technologies Inc. | Method and apparatus enabling synchronous transfer mode and packet mode access for multiple services on a broadband communication network |
US6404887B1 (en) * | 1998-06-24 | 2002-06-11 | Mci Communications Corporation | Intra-call control of ancillary telecommunications equipment |
US6731740B1 (en) * | 2001-06-21 | 2004-05-04 | At&T Corp. | Method for preventing overload condition in a circuit switched arrangement |
US6826273B1 (en) * | 2001-06-21 | 2004-11-30 | At&T Corp. | Method for preventing overload condition in a circuit switched arrangement |
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US20060188079A1 (en) * | 2003-01-08 | 2006-08-24 | Jiashun Tu | Method of controlling the user calling load in soft switch system |
US7577242B2 (en) * | 2003-01-08 | 2009-08-18 | Zte Corporation | Method of controlling the user calling load in soft switch system |
US20080059554A1 (en) * | 2006-08-29 | 2008-03-06 | Dawson Christopher J | distributed computing environment |
US8903968B2 (en) * | 2006-08-29 | 2014-12-02 | International Business Machines Corporation | Distributed computing environment |
US20120039167A1 (en) * | 2010-08-10 | 2012-02-16 | Qualcomm Incorporated | System, apparatus, and method for improving redial performance in wireless communication systems |
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